Decision Feedback Equalization (DFE) equalizes signal loss and interference on a signal. This signal loss and interference is often caused by a channel between the source of the signal and the receiver of that signal.
Not only may a channel cause signal loss and interference, this loss and interference may be different for different channels, change for a particular channel, and depend on the transmission rate of the signal. In part because of this, a particular equalization cannot accurately be set without taking into account the particular channel or, even for a particular channel, without an ability to change in response to changes in the loss or interference caused by that channel. DFE addresses this by making decisions about how to equalize loss and interference based on the signals received from the source and through the channel (this is a type of feedback). In effect, DFE continues to adapt based on the signals received to take into account the particular channel and changes to that channel.
A DFE's ability to accurately equalize for loss or interference depends on the signal's randomness. A random signal, also called a white signal, is one that has or can be closely approximated to have a random distribution of frequencies within a frequency band at which the signal is transmitted. Conversely, a non-random signal is typically referred to as a colored signal. A DFE is less accurate for a colored signal in part because the color of the signal may be confused with loss or interference caused by the channel.
Many signals transmitted today—especially those transmitted at comparatively high data-transmission rates—are not simply white signals. They are colored signals. As noted above, the more colored a signal, the less accurate current DFEs may equalize that signal.